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Bring Back 1962-63

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About Bring Back 1962-63

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  1. Bring Back 1962-63

    The Arctic Thread

    Hi MIA, a big welcome to 33andrain. Malcolm @Blessed Weather and I will be doing a lot of cross-posting on both forums, especially our Arctic and Teleconnection thread posts. You'll find it really friendly on "33". There are two great young hosts who set up this forum and they both post on here quite regularly. They are Geoff @33andrain and Pat @NJwxguy78. They provided all the facilities for us to create and build up the portal with full editing rights. Zac @Snowy Hibbo introduced us to this forum back in March and he created the Teleconnections thread on here. You'll recognise several other names on here too. I shall look forward to your posts and some interesting debates - Malcolm and I both really want to encourage that and we all have the Arctic as one of our favourite topics. David
  2. Bring Back 1962-63

    The Arctic Thread

    EXTREMELY SLOW ICE BUILD UP - THE RE-FREEZE HAS HARDLY BEGUN I shall be posting on here very frequently from now on with my main focus switching from the hurricane thread to this thread. I'll start with the latest ice extent charts. Arctic sea ice is running far below the 30 year mean - nothing surprising about that. The re-freeze has been quite fast in the west on the Canadian side but has barely started on the Siberian side and ice extent has even declined further in the Kara Sea! To compare the exact date (October 12th) with 2017, I show the NOAA chart below (the October 2017 NSIDC archive report shows a chart to October 5th). Note that the ice sheet last year (still well below the mean) did extend right across to the Siberian coast (more below). This summer we saw even more older ice thinning and melting (as has been highlighted in several earlier posts on here). Note how little (white areas) 100% ice concentration there is, even around the pole. 2018 ended up as only the 6th lowest on record (see below) following a slow down in melting through August - it had been challenging the record low year of 2012 before then. Unfortunately, with such little re-freezing, 2018 is heading for the lowest mid/late October extent on record (for that date). 2012 was recovering quickly through October. Weather and circulation patterns vary considerably and these can impact on ice build up in the short term but there are other factors in play, such as the anomalously high SSTs in the Arctic, particularly on the Atlantic side - I'll examine these again in my next post on here. Here we can see that 2012 was way below any other year but it reached its minimum extent in mid September. At that time, 2018 was the 6th lowest equalling 2008 (note that the previous 4 years + 2012 are shown but 2013 and earlier years are not as this chart is meant to be a 5 year comparison measured against the record low year). 2018 saw its lowest point in late September but has been slower to rise than in any of the earlier years. 2016 also had a slow recovery and that year saw the lowest extent on record from mid October and through into early winter. It looks like 2018 will see even lower levels within a few weeks unless a rapid re-freeze gets going very soon. This from the NSIDC report: Arctic sea ice extent for September 2018 averaged 4.71 million square kilometers (1.82 million square miles), tying with 2008 for the sixth lowest September in the 1979 to 2018 satellite record. This was 1.70 million square kilometers (656,000 square miles) below the 1981 to 2010 average, and 1.14 million square kilometers (440,000 square miles) above the record low recorded for September 2012. Prior to September 19, sea ice extent declined at a relatively rapid 14,440 square kilometers (5,580 square miles) per day, significantly faster than in most years. The near-zero loss rate between September 19 and 23, and the very late onset of significant seasonal ice growth after September 23, were atypical of the satellite record. Sea ice loss during the first half of September primarily occurred within the East Siberian, northern Laptev, and northern Chukchi Seas, in part because winds from the south brought warm air into the region and inhibited ice from drifting or growing southward. Retreat in these areas was partially offset by ice expansion in the eastern Beaufort Sea and the northern Kara and Barents Seas. The old ice that had been persisting in the Beaufort Sea near Prudhoe Bay mostly melted out by the end of September. While the Northern Sea Route opened again this year, as it has every year since 2008, ice lingered in the central section of the southern route of the Northwest Passage between Bellot Strait and Gjoa Haven. Since the seasonal minimum extent, reached on September 19 and again on September 23 at 4.59 million square kilometers (1.77 million square miles), ice cover has expanded in the Canadian Archipelago, the northern Chukchi and Beaufort Seas, and the East Greenland Sea, while retreating slightly within the Kara Sea. We can examine the circulation patterns and the other reasons for the unusually slow build up on here. For the Siberian coast to be ice free and for the entire eastern Arctic to be navigable in mid October is almost unheard of. I hope to bring some better news before too long but I am really concerned about this delayed re-freeze. David
  3. Bring Back 1962-63

    ***Winter Countdown Thread 2018-2019***

    Hi Zac, I assume that you have checked the NOAA snow cover maps on : https://www.ncdc.noaa.gov/snow-and-ice/snow-cover/ea/20181012 Here's Asia up to yesterday - running slightly above the 1981-2010 30 year mean (but slightly below the 1971 2000 mean and well below the decadal average which has seen a predominance of early Asian snow cover build ups) this year in N Siberia and above in central/S Asia/Mongolia/Tibet..... ...but well below the levels for last year in N Asia which saw very early build up in Siberia but conversely, very little further south. Judah Cohen himself has started to admit that his correlation theory between early Asian snow cover build up in October and later SSWs is not quite as strong as he first thought - basically it's rather more complex. However, there are some more recent theories that strong early winter cold in both Asia and N Am with a warming Arctic is starting to affect the strength and position of the jet stream and other circulation patterns - not just the weaker temp contrasts with the N Atlantic and NPAC oceans but almost a re-positioning of the poles (not literally of course) with much colder relative conditions displaced into the northern continental land masses. Quite a lot of research right now into the impact on the SPV. This is a such a complex area that we need to be cautious about any papers jumping to conclusions (re: global warming politics at either end of the climate change debate). We'll be covering this in the coming weeks and months on the new Arctic thread - where I will spend a lot more of my time once the hurricane season is over! We'll review some excellent papers on there. Note in the charts above, that current Arctic ice is well below the 2017 levels on the Siberian side. David EDIT: I'm sure you're all on top of this anyway but I'll add this and last year's US snow cover maps to complete the comparison: Fairly well ahead. I also noted that Hudson Bay SSTs have been running around 5c below the 1981-2010 mean for the last couple of months - so, given the right conditions, it might freeze over much earlier than last winter.
  4. Bring Back 1962-63

    2018 Atlantic Hurricane Season

    HAS MICHAEL MARKED THE END OF THE ATLANTIC HURRICANE SEASON? I am about to return from my business trip and I'm producing this post from my lap top without all my usual links to charts etc but I wanted to make the following points about the remainder of the hurricane season: The SSTs across all 4 Nino regions are the highest that they have been all season and the tropical Atlantic has already responded with another lull in activity. Although another setback in the progress to a weak El Nino is still possible, "if" this happens with the usual 10 to 14 day time lag response, we would be into November - when hurricane developments becoming increasingly rare. African easterly wave (AEW) activity greatly reduces during the fall as the African convection activity steadily migrates southwards and the dry season gets underway in the northern tropics. Nadene formed off shore and was probably the last AEW development of 2018. A couple of models do take her remnants into the Caribbean with a Tropical Storm reforming, although this seems unlikely. The models do show several minor systems in the tropical Atlantic but nothing really significant (up to yesterday's output). Mid Atlantic activity, which has been at record levels all season, may still produce 1 or 2 further developments. Hurricane Leslie is about to hit Portugal and Spain as a Tropical Storm. The main development region (MDR) migrates much further west towards the end of the season into the Caribbean and GoM. STTs across the tropical Atlantic and in the GoM (which only fell slightly when Michael churned up the surface layers) are currently above average and remain conducive to assisting the development of any new disturbances (not withstanding other factors). The Central American Gyre (CAG) which was largely responsible for spawning Michael can be active through October and November. The CAG has weakened (at least temporarily) with the low level easterlies taking EPAC developments westwards replacing the south west monsoon type flow slightly further north. There is currently a weaker CAG further south in the SW Caribbean which remains under surface south westerlies. There are signs of systems getting closer to Central America in two weeks or so. Whether the CAG develops and expands northwards again is not certain at this stage. CAGs really require the MJO to be in phases 8, 1 or 2 to produce substantial convective activity (as shown in the CAG paper that I reviewed on here recently). The MJO was in decent amp phase 1 during Michael's development. It is now in phase 2 and is moving towards the COD. In 10 days+, GEFS do show it re-emerging into phase 8 or 1 at decent amp again. So this, along with an extensive CAG setting itself up again, will be one to monitor towards the final week in October. Even if a CAG does spawn another development, it is by no means certain that it will make it up to named storm status let alone a hurricane and the track may be different as well as the upper conditions. Meanwhile, the EPAC may well see several new late season developments as that region is likely to respond favorably to the higher Nino region SSTs. Overall, the 2018 hurricane season has been extraordinary in so many ways and we cannot rule out one last surprise. Later next month I'll produce a hurricane season review. (unless someone else does one of course). David
  5. Bring Back 1962-63

    Historic Category 4 Hurricane Michael

    150 mph 000 WTNT64 KNHC 101528 TCUAT4 Hurricane Michael Tropical Cyclone Update NWS National Hurricane Center Miami FL AL142018 1030 AM CDT Wed Oct 10 2018 ...MICHAEL STILL STRENGTHENING AS THE EYE NEARS THE COAST OF THE FLORIDA PANHANDLE... Data from an Air Force Reserve Hurricane Hunter aircraft indicate that the maximum sustained winds have increased to near 150 mph (240 km/h) with higher gusts. The aircraft also reported that the minimum pressure has fallen to 923 mb (27.26 inches). The Apalachicola airport recently reported a wind gust of 72 mph (101 km/h). Water levels continue to rise quickly along the coast of the Florida Panhandle. A National Ocean Service water level station at Apalachicola recently reported over 5 feet of inundation above ground level. SUMMARY OF 1030 AM CDT...1530 UTC...INFORMATION ----------------------------------------------- LOCATION...29.5N 85.9W ABOUT 50 MI...80 KM SSW OF PANAMA CITY FLORIDA ABOUT 55 MI...90 KM WSW OF APALACHICOLA FLORIDA MAXIMUM SUSTAINED WINDS...150 MPH...240 KM/H PRESENT MOVEMENT...NNE OR 15 DEGREES AT 14 MPH...22 KM/H MINIMUM CENTRAL PRESSURE...923 MB...27.26 INCHES $$ Forecaster Brown
  6. Bring Back 1962-63

    Historic Category 4 Hurricane Michael

    I wish I had time to get involved in this thread but alas not this week. I just skimmed through and I didn't see the "water vapour" satellite image which does reveal a few other aspects. Note just how much the eye has cleared during the last couple of hours - really large and well defined and this is quite typical of an upper cat 4 or cat 5 system and we're in that region. Then note the large volume of moisture being sucked into the system from the south west. The "CAG" (Central American Gyre) where Micheal formed to the east and another disturbance from the west pushed into and then crossed Central America (with some huge rainfall totals there) from the EPAC is still responsible for this excessive moisture feed. This, amongst other factors, has been helping to sustain Michael. It really does look like he'll maintain his current intensity (possibly increasing fractionally more) right up until landfall. If I had more time, I would be reporting on the previous GoM major hurricanes to make landfall. Michael is yet another record in this highly unusual Atlantic and EPAC hurricane season. David
  7. Bring Back 1962-63

    2018 Atlantic Hurricane Season

    000 WTNT64 KNHC 071653 TCUAT4 Tropical Storm Michael Tropical Cyclone Update NWS National Hurricane Center Miami FL AL142018 1155 AM CDT Sun Oct 07 2018 ...DEPRESSION STRENGTHENS TO A TROPICAL STORM... Satellite wind data indicate that the depression has strengthened into Tropical Storm Michael. The maximum winds are estimated to be 40 mph (65 km/h) with higher gusts. An Air Force Reserve Hurricane Hunter aircraft is currently en route to investigate Michael. SUMMARY OF 1155 AM CDT...1655 UTC...INFORMATION ----------------------------------------------- LOCATION...19.2N 86.9W ABOUT 90 MI...145 KM S OF COZUMEL MEXICO ABOUT 225 MI...365 KM SW OF THE WESTERN TIP OF CUBA MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H PRESENT MOVEMENT...N OR 360 DEGREES AT 5 MPH...7 KM/H MINIMUM CENTRAL PRESSURE...1004 MB...29.65 INCHES $$ Forecaster Brown Ok - one more. Michael is born. David
  8. Bring Back 1962-63

    2018 Atlantic Hurricane Season

    I shall be away on business for the next week - so very little posting from me. I'll leave you with these satellite images. David Tropical depression 14 should be TS Michael within a few hours. Look at the closed circulation and spinning really getting going now. Also note that the remnants of 97E which pushed some exceptionally heavy rain across Central America on the "CAG" is rapidly being absorbed into TD14 on its south western edge. Meanwhile Invest 92L, well to the east of TS Leslie between the Canary and Azores islands is also showing signs of developing a closed circulation. This is predicted to move east and its convectivity may get into the west Med later this week and with further medicane potential forecast, this might add a bit more umph!
  9. Bring Back 1962-63

    2018 Atlantic Hurricane Season

    INVEST 91L IS NOW POTENTIAL CYCLONE 14 AND "MICHAEL" SEEMS TO BE ON HIS WAY It looks like "Michael" will be named as the next Atlantic tropical storm by the end of this weekend. Ex 97L has now moved inland and is crossing Central America with intense rainfall and severe flash flooding (please refer to my last post for details of this significant CAG event). David
  10. Bring Back 1962-63

    2018 Atlantic Hurricane Season

    A LITTLE MORE ON CENTRAL AMERICAN GYRES Steve @Superstorm93 and I have mentioned CAGS (Central American Gyres) in several of our recent posts and I felt that it might be useful to learn a little more about them. There are several excellent but pretty technical papers on this phenomena. I'll look into one of them briefly now but I'll save a more detailed review for the Teleconnections thread when I have more time. I just placed this paper into the Research Portal: A Climatology of Central American Gyres There you'll find an abstract and a link to the full paper which was published in 2017. I'll just list a few of the facts from the study and from the conclusions and then I'll show why the current pattern is a classic set up for perhaps some more prolonged GoM storm activity. CAGs are large, cliosed cyclonic circulations that occur over Central America and are similar to monsoonal low pressure systems that form in other ocean basins They only develop during the rainy season (May–November), mainly in May/June and especially from September to November 47 examples of CAGs were identified during the study focus period from 1980 to 2010 - roughly 1 to 2 examples per year but with wide variations in numbers in each season 12 developed in the EPAC, 12 over Central America and 23 over the Caribbean and/or GoM Another 98 examples of monsoonal type depressions were identified but without significant "closed circulation" cyclogenesis There are two types of CAGs - baroclinic and non-baroclinic CAGs are preceded by anomalous westerly lower-tropospheric flow in the eastern Pacific before their development (as we have been seeing) This is linked to a climatological reduction in easterly trade winds and is coincident with MJO phases 1, 2, and 8 (see below) Extreme precipitation is observed over multiple days in all known CAG cases, mostly along the Central American coastline (on both sides but see my comments below) There are a number of examples of tropical storm cyclogenesis in the north west Caribbean and western GoM caused directly by CAGs including in quiet hurricane seasons Named storms include Frances (1998) and Nicole (2010) but there are others too Baroclinic CAGs have a greater northward component (just as predicted for 97E and 91L) Trough and ridge patterns are described (and they seem to fit perfectly into the current set up) The higher topography of Central America plays a critical role in the generation and organization of convection and precipitation associated with a CAG event Gaps in the elevated terrain of Central America (Chivela Pass, Gulf of Papagayo & Gulf of Panama) are known to generate low-level vorticity (there are other studies on "Gap" winds) The study goes into a lot more detail but I'll make some comments now that relate this research to our current set up. No two CAG events are the same but the general characteristics are important. The baroclinic nature of this CAG event is already showing its hand. We should not underestimate the development potential for Invest 97E. The intense rainfall and thunderstorms are predicted to cross Central America during the next few days. Any significant cyclogenesis will not occur until this storm area moves out into the north west Caribbean or south west GoM. NHC only goes up to 5 days - their EPAC forecast now gives 0% chance of development but that's for the EPAC. If you read their tropical discussion and also look at the Tropical Tidbits track and intensity charts (which I posted 2 days ago on here), they have changed little and still show the north north eastward crossing from the EPAC into the GoM with the development potential. Furthermore, this more south westerly or westerly lower tropospheric monsoonal flow should help to clear the adverse wind shear ahead of it. So that and the remaining dry air being cleared away, is all assisting with later developments during next week and beyond. Even if 97E doesn't directly develop into a named storm it will push enormous amounts of moisture and convective activity into the GoM and priming it for further developments. The CAG can last for several weeks and it's very possible that it will spawn further developments increasing the likelihood of at least one or two named storms and perhaps hurricanes. 91L - on the eastern side and 97E - still on the western side but about to cross over may just be the beginning of several weeks of fascinating activity. Finally, just as the paper demonstrated, we have the MJO in phase 1 at decent amplitude - 8, 1 and 2 being an essential ingredient to assist CAG formations. David
  11. Bring Back 1962-63

    A Climatology of Central American Gyres

    A Climatology of Central American Gyres Authors: Philippe P. Papin, Lance F. Bosar, and Ryan D. Torn Published: 2nd May, 2017 Abstract: Central American gyres (CAGs) are large, closed, cyclonic circulations that occur during the rainy season (May–November), which can yield exceptional rainfall leading to catastrophic flooding and large societal impacts. A reanalysis-based climatology of CAGs is developed from an algorithm that distinguishes CAG cases from other systems. This algorithm identified CAG cases based on circulation intensity, a broad radius of maximum winds, and the existence of closed, Earth-relative, cyclonic flow. Based on these criteria, 47 CAG cases were identified from 1980 to 2010, featuring a bimodal distribution of cases with maxima in May–June and September–November. CAG cases are composited into two categories based on their upper-tropospheric PV structure: nonbaroclinic CAGs are more common (N = 42) and characterized by an upper-tropospheric anticyclone, while baroclinic CAGs are less common (N = 5) and characterized by an upper-tropospheric trough. Whereas a nonbaroclinic CAG has anomalous moisture and precipitation surrounding the center, a baroclinic CAG has anomalous moisture and precipitation concentrated east of the center, with these structural differences attributed to their upper-tropospheric PV structure. Both nonbaroclinic and baroclinic CAGs are preceded by anomalous westerly lower-tropospheric flow in the eastern Pacific before their development, which is linked to a climatological reduction in easterly trade winds and is coincident with MJO phases 1, 2, and 8. Extreme precipitation is observed over multiple days in all available CAG cases, most commonly along the Central American coastline and on average over a large fractional area (25%) within 10° of their center. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/MWR-D-16-0411.1
  12. Bring Back 1962-63

    2018 Atlantic Hurricane Season

    INVEST 91L + INVEST 97E - A FASCINATING CENTRAL AMERICAN GYRE COMBO We now have Invest 91L (as Steve @Superstorm93 mentions above) as a potential development somewhere in the north west Caribbean or south west GoM but we also have Invest 97E (which I referred to on here yesterday) also as a potential development in the EPAC as part of the central American gyre - in the same large area of convergence and convective activity. This is part of a wider band of activity that extends from 100W to 55W and from 7N in the south west to 22N in the north east. One, two or more disturbances "may" develop somewhere in the vicinity during the next few days and one to two weeks. If the EPAC 97L does develop it is predicted to cross over Nicaragua as an area of heavy rain and thunderstorms. Then, when it hits the south west GoM it may develop into a tropical depression. It is quite possible that the two systems will merge as they start to develop. It is still uncertain just to what extent they will develop and we are probably looking beyond 5 days to see any more definite cyclogenesis (which is outside the NHC prediction period). A broad area of low pressure centered near the northeastern coast of Honduras is drifting northwestward and producing disorganized shower and thunderstorm activity from Central America east-northeastward across the Western Caribbean to Hispaniola. Although strong winds aloft persist just to the north of the system, the upper-level environment is expected to be conducive enough to allow slow development. A tropical depression could form by late this weekend or early next week over the northwestern Caribbean Sea or Gulf of Mexico while the system moves northwestward to northward. Regardless of tropical cyclone formation, this disturbance will continue to bring torrential rains primarily to portions of Central America and the Yucatan peninsula during the next few days. * Formation chance through 48 hours...medium...40 percent. * Formation chance through 5 days...high...70 percent. TROPICAL DISCUSSION: A large cyclonic gyre is over the western Caribbean centered just off the NE coast of Honduras near 16N84W. A surface trough extends from 21N84W to the center to 09N82W. Scattered moderate to numerous strong convection is from 12N-19N between 77W-83W. Scattered moderate to isolated strong convection is over the Gulf of Honduras from 15N-18N between 85W-89W. A tropical depression could form by late this weekend or early next week over the northwestern Caribbean Sea or Gulf of Mexico while the system moves northwestward to northward. Regardless of tropical cyclone formation, this disturbance will continue to bring torrential rains primarily to portions of Central America and the Yucatan peninsula during the next few days. There is a medium chance of tropical cyclone formation within 48 hours. The position, track, intensity and timing of 97L has changed very litle since yesterday - so please refer to my previous post for that. This is the latest NHC advisory: The broad area of low pressure located offshore of the Pacific coast of southern Nicaragua has become a little better defined during the past several hours. This system is expected to drift northward or northwestward over the weekend, and gradual development is possible before it moves onshore the coast of Central America. Regardless of development, heavy rains could cause flash floods and mudslides in mountainous areas of western Costa Rica, Nicaragua, Honduras, El Salvador, and Guatemala through early next week. * Formation chance through 48 hours...low...30 percent. * Formation chance through 5 days...low...30 percent TROPICAL DISCUSSION: Broad 1007 mb low pressure is near 11.5N87.5W with scattered moderate and isolated strong convection within 60 nm in the E semicircle and within 120 nm in the W semicircle. Fresh to strong SW monsoonal flow and 8 to 12 ft seas, are expected roughly from 06N to 12N and E of 95W the next few days in response to a larger and more broad area of low pressure over Central America, called a Central American Gyre. As is typical for these features, the associated long fetch of SW winds across the tropical Pacific will transport abundant moisture into portions of Central America, especially from Costa Rica to Honduras. This will create the potential for significant rainfall over these areas through early next week. Refer to your local meteorological service for specific information on this potentially dangerous weather pattern. The models are likely to really struggle with this set up and we'll need to monitor it very closely. We could see anything from just some rather more organised thunderstorm activity right through to a hurricane. One or two named storms are possible. All the time, these systems will be pumping a lot of very humid air into the GoM. This may result in extending the period for a possible development by quite a few more days. There is still likely to be some adverse wind shear conditions but not as bad as we've seen recently. So, the next week or two weeks "may" see an interesting finale to the 2018 Atlantic hurricane season - although we cannot rule out one or two late October or even November developments. David
  13. Bring Back 1962-63

    Teleconnections: A More Technical Discussion

    LONGER TERM SEA SURFACE TEMPERATURE CHANGES Hi Tom @Isotherm I'm really interested with what you show above and entirely agree with your comments. Here we can move away from the short to medium term atmosphere/ocean coupling influences (AAM, GWO, Kelvin waves, MJO and ENSO) and examine the longer term changes and trends. Of course ENSO phases can still produce long lasting influences and very powerful shorter term events can have a legacy lasting over a few years (more below). We need to look down at the deeper ocean currents and also up at solar activity as two primary drivers of longer term SST changes and our understanding of both of these, although seeing major advances, still has a long way to go. Accepting that there will always be slight inconsistency over measures, means, time periods etc and not to mention all the very short term fluctuations, we are looking for trends. The last 3 months has been pretty flat roughly between + 0.1c and + 0.3c and well within the range shown on Tom's chart above for all of 2018. So, where do we go from here? Tom, you mentioned that the NHEM was still "running quite warm" which it is but let's consider this. The "average" conditions are strongly influenced by several very warm areas. We know that the Arctic is running at huge +ve anomalies and that's partly a legacy of the 2015/16 super El Nino with a powerful PV and the relentless south west/north east Atlantic jet stream pumping warm waters right up to the edge of Arctic ice sheet. Unfortunately, it may take several years of more favourable patterns in the Arctic until we see those anomalies fall back significantly. Then, this summer we've had a string of powerful typhoons which have pumped up some very warm waters into the far NPAC. That anomalous warm pool in the western Atlantic has started to contract. The central and west Mediterranean still has well above average SSTs as part of the legacy of the widespread mid-latitude NHEM hot summer but other mid lat SSTs have eased back to some extent. This chart confirms the extremely +ve SST anomalies "locked" into the Arctic. The dark browns are over +4c and those olive patches (such as west of Svalbard) are over +8c anomalies. Now if we remove the extremes, we could easily say that the NHEM would be running below average! This is not an anti climate change use of statistics but helps us to look for the "main" underlying trends. If we do see an El Nino developing later this fall and into the winter, a weak event should not have such a widespread extended influence on SSTs beyond the tropics. We've seen that anomalous cold pool in the north west Atlantic for several years now and there have been a number of papers written about that. That was, however, confined to a small patch around and to the south of the southern tip of Greenland and slightly westwards and south westwards from there. Earlier this summer, we saw that cold pool start to expand. This seemed to be in a response to the NHEM patterns - while the middle latitudes saw all that warmth, further north it was colder than usual (Iceland saw one of their coldest summers for many years). As the warmth further south eased and the NHEM patterns changed, North Atlantic SSTs did very briefly recover to nearer neutral but they have fallen back again to some extent. Not only that but the cold pool has now greatly expanded in all directions and stretches across the whole of the North Atlantic from roughly 50N to 70N (as shown in the map above). Obviously short term influences can distort the trend in either direction but overall it does look like the NHEM "may" join the SHEM with global SST anomalies "perhaps" turning -ve. Time will tell but we now need to examine the primary causes, the deep ocean currents and solar influences. In particular we should focus on the natural variability in the longer term oscillations such as: The AMO - the Atlantic Multidecadal Oscillation (also known as the AMV - Atlantic Multidecadal variability) The PDO - the Pacific Decadal Oscillation (the PMO - Pacific Multidecadal Oscillation and the IPO - Interdecadal Pacific Oscillation) The PCO - the Pacific Centennial Oscillation We already have a few excellent papers on these in the Research Portal and these (and others) can be reviewed on here. We have discussed longer term SSTs in bits and pieces over the last few months on the Teleconnections thread, in ENSO posts, Malcolm @Blessed Weather and I on several hurricane thread posts (the AMO in particular) and Tom on the Countdown thread (as well as in a number of PM exchanges). I would like us (all those who are interested) to get our SST analyses, views and comments coordinated on this Teleconnections thread. Just as we did with the ENSO debate, we can develop this in the coming days, weeks and months. We can examine the facts in a balanced way without all the hype at either end of the climate change debate. David
  14. Bring Back 1962-63

    2018 Atlantic Hurricane Season

    THIS IS GETTING INTERESTING We have an unusual twist to a potential GoM development with Invest 97E. This is a development in the EPAC which is predicted to push across into the north west Caribbean and may merge with the convective activity there. Something that Steve @Superstorm93 alluded to yesterday. NHC only go up to day 5. So, let's start with the Invest charts. A broad area of low pressure located offshore of the Pacific coast of southern Nicaragua continues to produce disorganized showers and thunderstorms. This system is expected to drift northward or northwestward during the next several days, and some slow development is possible if it remains offshore the coast of Central America. Regardless of development, heavy rains could cause flash floods and mudslides in mountainous areas of western Costa Rica, Nicaragua, Honduras, El Salvador, and Guatemala through early next week. * Formation chance through 48 hours...low...20 percent. * Formation chance through 5 days...low...30 percent. Discussion: The monsoon trough will meander between 09N and 12N, with fresh to strong SW winds and building seas expected S of the monsoon trough E of 100W through Sat in response to broad low pressure over the western Caribbean and Central America. This broad area of low pressure and the associated long fetch of SW winds across the tropical Pacific will transport abundant moisture into portions of Costa Rica, Nicaragua, and western Panama, and will produce significant rainfall through early next week. Isolated areas could see 20 inch rainfall accumulations by Mon. Refer to your local meteorological service for specific information on this potentially dangerous pattern. The original patch of convection in the north west Caribbean now has a 60 % chance of development. An area of low pressure located near Cabo Gracias a Dios on the eastern border of Honduras and Nicaragua is accompanied by an extensive area of disturbed weather extending from Central America eastward across Hispaniola. Although strong winds aloft are located just to the north of this system, the upper-level environment is expected to be conducive enough to allow for some development, and a tropical depression could form by late this weekend or early next week over the northwestern Caribbean Sea or southern Gulf of Mexico while the system moves slowly northwestward. Regardless of tropical cyclone formation, this disturbance will continue to bring torrential rains primarily to portions of Central America and the Yucatan peninsula during the next few days. * Formation chance through 48 hours...low...20 percent. * Formation chance through 5 days...medium...60 percent. This is a fascinating and complex EPAC/Atlantic combination and will pump plenty of moisture into the GoM. David
  15. Bring Back 1962-63

    2018 Atlantic Hurricane Season

    Now Geoff, please do not get too excited but NDC are just starting to up their interest! Still not sufficiently for an "Invest" but we "may" see that quite soon. ZCZC MIATWOAT ALL TTAA00 KNHC DDHHMM Tropical Weather Outlook NWS National Hurricane Center Miami FL 200 PM EDT Thu Oct 4 2018 For the North Atlantic...Caribbean Sea and the Gulf of Mexico: The National Hurricane Center is issuing advisories on Hurricane Leslie, located over the central Atlantic Ocean. 1. A broad low pressure area centered near the northeastern coasts of Nicaragua and Honduras is producing an extensive area of disorganized clouds and thunderstorms over the central and western Caribbean Sea, as well as portions of Central America. While surface pressures are relatively low in the area, upper-level winds are currently not favorable for tropical cyclone formation. Environmental conditions could become less hostile by late this weekend or early next week, and a tropical depression could form as the system moves slowly northwestward across the northwestern Caribbean Sea and the southern Gulf of Mexico. * Formation chance through 48 hours...low...near 0 percent. * Formation chance through 5 days...medium...40 percent. Forecaster Beven CARIBBEAN SEA... A large cyclonic gyre, defined by a broad area of low pressure, covers a portion of Central America and the western Caribbean Sea. Within this gyre, a surface trough is analyzed from 20N80W to a 1007 mb low near 16N83W to 11N83W. Satellite imagery shows scattered moderate to isolated strong convection from 11N-16N between 75W-82W. Scattered showers and thunderstorms are noted elsewhere from 11N-18N between 70W-85W. Some slow development of this system is possible this weekend or early next week as the system drifts northwestward across the northwestern Caribbean Sea and the southern Gulf of Mexico. This has increased from 20% chance 2 days ago to 30% chance yesterday and now 40%. There's still a long way to go. Even if this disturbance does get more organised, it'll still have that troublesome adverse wind shear to negotiate. if this does development into a Hurricane then you and the Navy can have the forecaster of the month award David EDIT: At this stage, the convective activity is very disorganised (and still dies down overnight) as can be seen below:
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